Piston pump

ABSTRACT

The invention relates to a piston pump ( 10 ) for a hydraulic vehicle brake system that has traction control. The invention proposes embodying the piston pump ( 10 ) with a piston ring ( 24 ), for instance a PTFE, which ring serves as both a sealing and a guide ring. The invention lessens the effort and expense of assembly as well as the production costs for the piston pump ( 10 ). To achieve reliable sealing, the invention proposes embodying the piston ring ( 24 ) with an internal cone on its side toward a pump chamber ( 18 ), so that during a pumping stroke, the piston ring ( 24 ) is subjected to pressure from the pump chamber ( 18 ) and is pressed into sealing contact against a pump bore ( 12 ).

SPECIFICATION PRIOR ART

[0001] The invention relates to a piston pump having the characteristics of the preamble to claim 1. The piston pump is intended in particular for pumping brake fluid in a hydraulic vehicle brake system.

[0002] Piston pumps of this kind are known in many versions. One example of such a piston pump for a hydraulic vehicle brake system is disclosed in German Patent Disclosure DE 197 12 147 A1. The known piston pump has a pump housing, with a pump bore in which a pump piston rests axially displaceably. For pumping brake fluid, the pump piston can be driven, for instance by means of an eccentric element, to execute a stroke motion that reciprocates axially in the pump bore. An axial portion of the pump bore forms a pump chamber of the piston pump, whose volume is alternatingly increased (reverse stroke) and decreased (pumping stroke) during the stroke motion of the pump piston. The piston pump pumps fluid (brake fluid) in a manner known per se.

[0003] For axial guidance of the pump piston in the pump bore on a side toward the pump chamber, the pump piston of the known piston pump has a guide ring. For sealing the pump chamber off, a sealing ring is provided on a side of the guide ring toward the pump chamber.

ADVANTAGES OF THE INVENTION

[0004] The piston pump of the invention having the characteristics of claim 1 has a piston ring, on a side of the pump piston toward the pump chamber, which ring seals off the pump piston at all times during the pumping stroke in the pump bore, and which axially displaceably guides the pump piston, on the end toward the pump chamber, in the pump bore. The piston ring of the piston pump of the invention accordingly forms both a sealing and a guide ring on the side of the pump piston toward the pump chamber. It suffices for the piston ring to seal off the pump piston in the pump bore during the pumping stroke, while sealing is unnecessary during the reverse stroke of the pump piston. The piston ring can for instance have a sealing cuff, which during the reverse stroke of the pump piston can have a spillover flow in the direction of the pump chamber. The piston ring can be axially retained on the pump piston or in the pump bore; that is, the piston ring can move along with the pump piston or can be held in stationary fashion in the pump bore.

[0005] The invention has the advantage that a single piston ring, on the side of the pump piston toward the pump chamber, suffices both for axially guiding the pump piston and sealing it off in the pump bore. The effort and expense for production and assembly are reduced as a result. Furthermore, an axial length required for sealing and axial guidance of the pump piston is reduced by the use of only one piston ring; the pump piston and the piston pump can be made axially shorter.

[0006] Advantageous refinements of and improvements to the invention defined by claim 1 are the subject of the dependent claims.

[0007] In claim 2, the piston ring in its axial portion has a circumferential face, which is subjected to fluid from the pump chamber. The axial portion is preferably oriented toward the pump chamber. The goal of this feature of the invention is that the fluid under pressure in the pump chamber during the pumping stroke of the pump piston acts upon the piston ring in the axial portion on the circumferential face and as a result presses the piston ring against a counterpart face, facing away from the acted-upon circumferential face of the piston ring, in order to achieve good sealing off of the pump piston during the pumping stroke. If the piston ring is retained axially on the pump piston and moves along with it, then the counterpart face, against which the fluid from the pump chamber presses the piston ring, is a wall of the pump bore, along which the piston ring slides during the stroke motion of the pump piston. The circumferential face acted upon by the fluid is an inner circumferential face of the piston ring. The circumferential face is limited to one axial portion of the piston ring, since the piston ring, over a further portion of its axial length, rests sealingly on the pump piston and is not subjected to fluid. If the piston ring is axially retained in the pump bore and does not move with the pump piston, then the counterpart face against which the fluid from the pump chamber presses the piston ring sealingly during the pumping stroke is an outer circumferential face of the pump piston, and in that case this pump piston slides axially in the piston ring. The circumferential face acted upon by the fluid from the pump chamber in the pumping stroke of the pump piston is in this case an outer circumferential face of the piston ring.

[0008] Claim 3 provides that the circumferential face acted upon by the fluid from the pump chamber is represented by a change in diameter of the piston ring at the inner or outer circumference of the piston ring. The change in diameter can be represented for instance as a conical face (claim 4) or as an annular step (claim 5) on the inner or outer circumference of the piston ring. This embodiment has the advantage that no change in diameter of the pump piston and/or in the pump bore in the region of the piston ring has to be provided so as to subject the piston ring in an axial portion to fluid from the pump chamber. This makes it simpler and less expensive to produce the pump piston and the pump bore.

[0009] In claim 6, the piston ring is embodied symmetrically to a radial center plane; that is, it has the diameter change, for representing the circumferential face acted upon by the fluid from the pump chamber, on both of its face ends. This embodiment of the invention prevents the piston ring from being installed wrong and largely precludes errors in assembly.

[0010] To attain a good sealing action, claim 7 contemplates an undersize of an inside diameter of the piston ring relative to the pump piston, and/or claim 8 contemplates an oversize of an outer diameter of the piston ring, relative to the pump bore. The undersize or oversize has the effect that the pump piston rests with initial tension on the pump piston or in the pump bore.

[0011] In claim 9, a free face is provided over part of an axial length of the piston ring, so that only over a portion of its axial length does the piston ring rest on the pump bore or on the pump piston. The free face reduces friction on the piston ring. The free face is provided axially outside the circumferential face of the piston ring that is acted upon by the fluid from the pump chamber.

[0012] The piston pump of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), VDC (vehicle dynamics control) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or VDC or EHB). The pump is needed for instance in a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB). With the wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.

DRAWING

[0013] The invention will be described in further detail below in terms of preferentially selected exemplary embodiments shown in the drawing. Shown are:

[0014]FIG. 1, a piston pump of the invention in axial section;

[0015]FIG. 2, an enlarged view of a piston ring of the piston pump of FIG. 1 shown in detail II in FIG. 1; and

[0016]FIGS. 3 and 4, two modified embodiments of piston rings of the piston pump of FIG. 1, in a view corresponding to FIG. 2.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0017] The piston pump 10 of the invention, shown in FIG. 1, is inserted into a graduated pump bore 12, which is mounted in a hydraulic block that forms a pump housing 14. The hydraulic block, of which in the drawing only a fragment surrounding the piston pump 10 is shown, is a component part of a traction-controlled hydraulic vehicle brake system not otherwise shown here. Inserted into it in addition to the piston pump 10 are further hydraulic components, such as magnet valves or pressure reservoirs, and they are hydraulically interconnected both with one another and with the piston pump 10 of the invention.

[0018] The piston pump 10 has a pump piston 16, one end of which, remote from a pump chamber 18, is guided with a guide ring 20 in the pump bore 12 and is sealed off with a sealing ring 22. The pump chamber 18 is an axial portion of the pump bore 12, on one end of the pump piston 16. A volume of the pump chamber 18 changes upon a stroke motion of the pump piston 16, and as a result the piston pump 10 pumps fluid in a manner known per se. A different end of the piston 16, remote from the pump chamber 18, is guided axially displaceably and sealed of by a piston ring 24, to be further explained below, in a bush 26 of the piston pump 10. The bush 26 is inserted with a press fit into the pump bore 12 of the pump housing 14. The press fit brings about sealing between the inlet and the outlet side, or in other words, the low- and high-pressure sides of the piston pump 10.

[0019] For the pump inlet, an axial blind bore 28 is made in the piston 16, beginning at a side toward the pump chamber 18, and this bore is intersected near its bottom by transverse bores 30. The blind and transverse bores 28, 30 communicate, via an end edge 32 of the bush 26 and through the pump bore 12, with an inflow bore 34, which is mounted radially to the pump bore 12 and, discharging into the pump bore, in the hydraulic block that forms the pump housing 14.

[0020] On a side of the piston 16 toward the pump chamber 18, there is a check valve in the form of an inlet valve 36. The inlet valve 36 has a valve ball 38 as its valve closing body, which cooperates with a conical valve seat 40, which is mounted at an orifice of the blind bore 28 of the piston 16. A helical compression spring as a valve closing spring 42 presses the valve ball 38 against the valve seat 40. The valve ball 38 and the valve closing spring 42 are received in a valve cage 44, which is produced as a tubular deep-drawn part of sheet metal, with a diameter corresponding approximately to the diameter of the piston 16, and which is provided with flow openings 46. The valve cage 44 has an annular step 48, with which it rests on a face end of the piston 16 oriented toward the pump chamber 18. Moreover, the valve cage 44 has a radial flange 50, which is integral with it and protrudes outward, against which a helical compression spring, as a piston restoring spring 52, presses, and in this way retains the valve cage 44 on the piston 16. At the same time, between itself and a support ring 56 braced on an annular shoulder 54 of the piston 16, the radial flange 50 also retains the piston ring 24 in the axial direction on the piston 16.

[0021] The piston restoring spring 52, via the radial flange 50 of the valve cage 44, presses the piston 16 in the axial direction against a circumference of an eccentric element 58, which can be driven to rotate by an electric motor and which serves in a manner known per se for driving the piston 16 to execute a reciprocating stroke motion.

[0022] On a side bordering the pump chamber 18, the bush 26 has a bush bottom 60, which is integral with it and in the middle of which a continuous outlet hole 62 of the piston pump 10 is mounted.

[0023] On a side remote from the pump chamber 18, a closure part 64 is mounted on the bush bottom 60. The closure part 64 takes the form of a cylindrical stopper. It is inserted into the pump bore 12 and is secured in the pump bore 12 and sealed off in fluid-tight fashion by means of a calking 66 of the pump housing 14. At the same time, the closure part 64 keeps the bush 26 in the pump bore 12.

[0024] On a face end toward the bush 26, a flat, preferably cylindrical recess 68 is made in the closure part 64, and the bush 26 is inserted into it by its bush bottom 60. For securing the closure part 64 to the bush 26, the bush 26, on its bush bottom 60 inserted into the closure part 64, has a radial collar 70 protruding outward past it, which forms an undercut 72 that is engaged from behind by a rim 74 of the recess 68 of the closure part 64. To put the rim 74 into engagement from behind with the undercut 72, it is reshaped radially inward, for instance by crimping. For securing purposes, crimping it at three to four points of the circumference suffices.

[0025] On a bottom of the recess 68, an axial blind bore 76 in the closure part 64 is made, in which a check valve as an outlet valve 78 is accommodated, which valve cooperates with a valve seat 80 that is made at an orifice, toward the closure part 64, of the outlet hole 62 in the bush bottom 60. In the blind bore 76 of the closure part 64, a valve ball 82 is inserted as a valve closing body, which is pressed against the valve seat 80 by a helical compression spring 84 acting as a valve closing spring.

[0026] As the pump outlet, a number of radial conduits 86 are made in an outside of the bush bottom 60 and discharge into an annular conduit 88, which is made on the bottom of the recess 68 of the closure part 64. From the annular conduit 88, outlet conduits 90 lead outward into a ring line 92, which encloses the bush bottom 60 in the pump bore 12. An outlet bore 94 that is made in the pump housing 14 discharges into the ring line 92.

[0027] The piston ring 24, shown enlarged in FIG. 2, has a dual function: It seals off the pump piston 16 in the pump bore 12 of the pump housing 14, and it guides the piston 16 axially in the pump bore 12. The piston ring 24 forms a sealing and guide ring. The piston ring 24 is made from a plastic (polytetrafluoroethylene, or PTFE). The piston ring 24 has an underside relative to the pump piston 64; that is, it is placed with initial tension and as a result sealingly on the pump piston 16. With respect to the pump bore 12, the piston ring 24 has an oversize, so that in this case as well, it rests with initial tension and as a result sealingly. Axially, the piston ring 24 is retained between the support ring 56 and the radial flange 50 of the valve cage 44. An axial play exists between the support ring 56 and the radial flange 50; the piston ring 24 is not prestressed axially. Since the piston ring 24 is retained axially between the support ring 56 and the radial flange 50 on the piston 16, the piston ring 24 moves along with the pump piston 16. Upon a stroke motion of the pump piston 16, the piston ring 24 slides along one wall of the pump bore 12, which forms a counterpart face 96 on which the piston ring 24 rests in sealed fashion. The piston ring 24 can for instance be reinforced with carbon fibers. By adding graphite, the sliding properties of the piston ring 24 can be improved.

[0028] In the embodiment of the invention shown in FIGS. 1 and 2, the piston ring 24 has an internal cone 98, on its face end toward the pump chamber 18. The internal cone 98 extends over a portion of an axial length of the piston ring 24. A jacket face of the internal cone 98 forms an inner circumferential face 100 of the piston ring 24, which, since the internal cone 98 is open toward the pump chamber 18, is subjected to brake fluid from the pump chamber 18. During a pumping stroke of the pump piston 16, brake fluid, put under pressure by the pump piston 16 in the pump chamber 18, exerts pressure on the inner circumferential face 100 of the piston ring 24 and as a result presses the piston ring 24 radially outward against the wall of the pump bore 12, which forms the counterpart face 96. By the exertion of pressure on the inner circumferential face 100, reliable sealing of the pump piston 16 in the pump bore 12, especially when the pumping pressure is high, is assured.

[0029]FIG. 3 shows a further refinement of the piston ring 24. This piston ring has an annular step 102 on the outer circumference, by which a gap 104 is formed between the piston ring 24 and the circumferential wall of the pump bore 12. The gap 104 is provided on a side of the piston ring 24 remote from the pump chamber 18. The gap 104 forms a free face, which reduces the friction on the piston ring 24. The free face is provided axially outside the internal cone 98 of the piston ring 24 and does not lessen the sealing action of the piston ring 24 as a result of the pressure exertion in the region of the internal cone 98.

[0030]FIG. 4 shows a further modification of the piston ring 24 of FIGS. 1 and 2. The piston ring 24 shown in FIG. 1 has internal cones 98 on both of its face ends. This makes the piston ring 24 symmetrical to its radial center plane, and it can therefore not be placed in the wrong direction on the piston 16. This embodiment precludes errors of assembly of the piston ring 24. The second internal cone 98 has no further significance.

[0031] As a further distinction from FIGS. 1-3, in FIG. 4 the piston 16 has an outward-protruding radial collar 106, integral with it, for axial bracing of the piston ring 24 on the pump piston 16. As a result, the support ring 56 is omitted. A conical chamfer 108 of the pump piston 16 at the transition from the radial collar 106 to the pump piston 16 supports the piston ring 24 on the internal cone 98 on the side of the piston ring 24 remote from the pump chamber 18, and as a result prevents an enlargement of the internal cone 98, acted upon by pressure, on the side of the piston ring 24 oriented toward the pump chamber 18, during operation of the piston pump 10. 

1. A piston pump, having a pump piston, which is drivable to execute an axially reciprocating stroke motion in a pump housing, and which in its stroke motion alternatingly increases (reverse stroke) and decreases (pumping stroke) a volume of a pump chamber, which pump chamber is an axial portion of the pump bore and is defined on one side by the pump piston, and having a piston ring, which is disposed on an end, toward the pump chamber, of the pump piston, characterized in that the piston ring (24) forms a sealing and guide ring that is not loaded in the axial direction and that in any case during the pumping stroke seals off the pump piston (16) in the pump bore (12), and which ring guides the pump piston (16) axially displaceably in the pump bore (12).
 2. The piston pump of claim 1, characterized in that the piston ring (24), in an axial portion, has a circumferential face (100) that is subjected to fluid from the pump chamber (18), and the circumferential face (100) faces away from a counterpart face (96) on which the piston ring (24) rests sealingly and relative to which the piston ring (24) is displaced during the stroke motion of the pump piston (16).
 3. The piston pump of claim 2, characterized in that the piston ring (24) has a diameter change, which brings about the subjection of the circumferential face (100) of the piston ring (24), in the axial portion of the piston ring (24), to fluid from the pump chamber (18).
 4. The piston pump of claim 3, characterized in that the piston ring (24) has a conical face, on its side toward the pump chamber (18).
 5. The piston pump of claim 3, characterized in that the piston ring (24) has an annular step as a diameter change.
 6. The piston pump of claim 3, characterized in that the piston ring (24) is symmetrical to a radial center plane.
 7. The piston pump of claim 1, characterized in that the piston ring (24) rests with initial tension on the pump piston (18).
 8. The piston pump of claim 1, characterized in that the piston ring (24) rests with initial tension in the pump bore (12).
 9. The piston pump of claim 1, characterized in that the piston ring (24) has a free face (105) on its circumference, over a portion of its axial length, with which face it does not rest on a counterpart face (96). 